N Korean boat intrudes, says S Korea

"A North Korean patrol boat crossed into the South's waters, as they oversaw Chinese fishing boats operating in the Yellow Sea," the ministry said in a statement.

"Our navy sent two patrol boats to chase the North Korean vessels back," the statement said.

The North Korean vessels stayed in South Korean waters for about 50 minutes, it added.

Sunday's case was the seventh violation of the maritime border this year.
North and South Korean naval vessels clashed in June 1999 in the Yellow Sea after North Korean torpedo and patrol boats escorted northern fishing boats to the demarcation line.

South Korea's navy sank one Northern vessel and heavily damaged several others in the worst naval clash between the rival Koreas since the 1950-53 Korean war.

North Korea has long disputed the Yellow Sea demarcation line, unilaterally drawn by the United Nations Forces when the Korean War ended in an armed truce that has left the two Koreas technically still at war.